No better illustration could probably be given of the danger of drawing conclusions when you are not in possession of all the facts. One thing was entirely overlooked in all this speculation until about twenty years ago,--that pneumonia was due not simply to the depressing effects of cold, but to a specific germ, the pneumococcus of Fraenkel. This threw an entirely new light upon our elaborate weather-causation theories. And while these still hold the field by weight of authority and that mental inertia which we term conservatism, yet the more thoughtful physicians and pathologists are now coming to regard these factors as chiefly important according to the extent to which we are crowded together in often badly lighted and ill-ventilated houses and rooms, with the windows and doors shut to save fuel, thus affording a magnificent hothouse hatching-ground for such germs as may be present, and ideal facilities for their communication from one victim to another. At the same time, by this crowding and the cutting off of life and exercise in the open air which accompanies it, the resisting power of our bodies is lowered. And when these two processes have had an opportunity of progressing side by side for from two to three months; when, in other words, the soil has been carefully prepared, the seed sown, and the moist heat applied as in a forcing-house, then we suddenly reap the harvest. In other words, the heavy crop of pneumonia in January, February, and March is the logical result of the seed-sowing and forcing of the preceding two or three months. The warmth of summer is even more depressing in its immediate effects than the cold of winter, but the heat carries with it one blessing, in that it drives us, willy-nilly, into the open air, day and night. And on looking at statistics we find precisely what might have been expected on this theory, that the death-rate for pneumonia is lowest in July and August. It might be said in passing that, in spite of our vivid dread of sunstroke, of cholera, and of pestilence in hot weather, the hot months of the year in temperate climates are invariably the months of fewest diseases and fewest deaths. Our extraordinary dread of the summer heat has but slender rational physical basis. It may be but a subconscious after-vibration in our brain cells from the simoons, the choleras, and the pestilences of our tropical origin as a race. Open air, whether hot, cold, wet, dry, windy, or still, is our best friend, and house air our deadliest enemy.